XY Ursae Majoris is a short period binary star system in the northern circumpolar constellation of Ursa Major. It is an eclipsing binary with a baseline apparent visual magnitude of 9.50.[3] The system is located at a distance of 221.5 light years from the Sun based on parallax measurements,[2] but is drifting closer with a radial velocity of −10 km/s.[6] It has a relatively high proper motion, traversing the celestial sphere at the angular rate of 0.191″·yr⁻¹.[10]

XY Ursae Majoris

A light curve for XY Ursae Majoris, plotted from TESS data[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ursa Major
Right ascension	09h 09m 55.935s[2]
Declination	+54° 29′ 17.72″[2]
Apparent magnitude (V)	9.50[3]
Characteristics
Evolutionary stage	Main sequence
Spectral type	G2V + K5V[4]
B−V color index	0.765±0.039[3]
Variable type	Detached eclipsing binary, RS CVn[5]
Astrometry
Radial velocity (Rv)	−9.98±0.83[6] km/s
Proper motion (μ)	RA: −49.781 mas/yr[2] Dec.: −182.641 mas/yr[2]
Parallax (π)	14.7223 ± 0.0137 mas[2]
Distance	221.5 ± 0.2 ly (67.92 ± 0.06 pc)
Absolute magnitude (MV)	5.41[3]
Orbit[7]
Period (P)	0.4789961 d
Semi-major axis (a)	3.05±0.01 R☉[8]
Eccentricity (e)	0.0
Inclination (i)	79.81[8]°
Periastron epoch (T)	2,453,821.6344±0.0002
Semi-amplitude (K1) (primary)	124.74±0.28 km/s
Details
Primary
Mass	1.01±0.01[8] M☉
Radius	1.22±0.01[8] R☉
Luminosity	1.10±0.02[8] L☉
Temperature	5,780[4] K
Secondary
Mass	0.65±0.01[8] M☉
Radius	0.58±0.01[8] R☉
Luminosity	0.09±0.01[8] L☉
Temperature	3,850[4] K
Other designations
XY UMa, AG+54 702, BD+55 1317, HD 237786, HIP 44998, SAO 27143, PPM 32024[9]
Database references
SIMBAD	data

The variability of this system was discovered by W. Strohmeier and its period was determined by R. Kippenhahn, with the findings announced in 1955.[11] It was found to be a detached eclipsing binary system, and by 1963 a variable primary component had been noted.[12] E. H. Geyer made intermittent light curve studies of the system starting with its discovery up until 1975,[11] ascribing variability in the light curve to star spot activity on the primary component. The orbital period of the pair was determined to be 0.479 d,[13] with the orbital plane inclined at an angle of 79.84° to the line of sight from the Earth.[8]

By 1990, enough data had been collected to identify a long term variation of the period, and it was hypothesized this was caused by a third body in the system orbiting the close binary.[14] The orbital period of this component was estimated to be ~30 years in 2001,[15] then refined to 26.7 years by 2010. If the orbital plane of this component is the same as the inner pair, its mass would be 18% of the mass of the Sun. An alternative solution to the period change suggests magnetic activity causes shifts in the angular momentum of the system, but this is considered less likely.[8]

This is a double-lined spectroscopic binary star system with an orbital period of 11.5 h.[7] The primary component is a G-type main-sequence star with a stellar classification of G2V.[4] It is an RS Canum Venaticorum-type variable that is magnetically active[5] and a bright X-ray source.[16] Despite this, relatively few optical flares have been observed.[16] The cooler secondary is a K-type main-sequence star of class K5V that is smaller and less massive than the primary.[4]

References

Further reading

На других языках

[ru] XY Большой Медведицы